Comparative Gene-Expression Analysis of Alzheimer's Disease Progression with Aging in Transgenic Mouse Model

Abstract

Alzheimer's disease (AD) is a multifactorial neurodegenerative disorder characterized by progressive memory dysfunction and a decline in cognition. One of the biggest challenges to study the pathological process at a molecular level is that there is no simple, cost-effective, and comprehensive gene-expression analysis tool. The present study provides the most detailed (Reverse transcription polymerase chain reaction) RT-PCR-based gene-expression assay, encompassing important genes, based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) disease pathway. This study analyzed age-dependent disease progression by focusing on pathological events such as the processing of the amyloid precursor protein, tau pathology, mitochondrial dysfunction, endoplasmic reticulum stress, disrupted calcium signaling, inflammation, and apoptosis. Messenger RNA was extracted from the cortex and hippocampal region of APP/PS1 transgenic mice. Samples were divided into three age groups, six-, nine-, and 12-month-old transgenic mice, and they were compared with normal C57BL/6J mice of respective age groups. Findings of this study provide the opportunity to design a simple, effective, and accurate clinical analysis tool that can not only provide deeper insight into the disease, but also act as a clinical diagnostic tool for its better diagnosis.

Keywords: Alzheimer’s disease; clinical diagnosis; dementia; gene expression.

Figure 1

Expression analysis of genes involved in amyloid precursor protein procession. (a) Histograms representing relative mRNA expression of Adam10, App, Lpl, Appb1, ApoE, Snca, Casp8, Psen1, Pen-2, Bace 1, Ide, Nep, Ncstn, and Aph1B. Represented values are the mean and SD obtained from three individual experiments performed for each sample. The line on the x-axis at 1.0 shows the gene expression of control samples. (b) Bar plots representing fold-change values represented in the log2 scale showing gene expression in the brain of six-, nine-, and 12-month-old samples. Baseline shows expression in control samples. (c) Scattered-dot plot shows gene expression involved in amyloid protein processing. * Expression is significantly different to wild type (WT) (p ≤ 0.05). n.s., Nonsignificant.

Figure 2

Expression analysis of genes involved in taupathology. (a) Histograms representing relative mRNA expression of Caln, Cdk5, p25, Nos1, Gsk3b, and tau. Represented values are the obtained mean and SD from three individual experiments performed for each sample. The line on the x-axis at 1.0 shows the gene expression of control samples. (b) Bar plots representing fold-change values represented in the log2 scale showing gene expression in the brain of six-, nine-, and 12-month-old samples. Baseline shows expression in control samples. (c) Scattered-dot plot shows gene expression involved in tau pathology. * Expression is significantly different to WT (p ≤ 0.05). n.s., Nonsignificant.

Figure 3

Expression analysis of genes involved in endoplasmic reticulum stress. (a) Histograms representing relative mRNA expression of Ryr3, ire1a, Ip3r, atf1, Psen1, Gq, Serca1, Plcb1, and Perk. Represented values are the mean and SD obtained from three individual experiments performed for each sample. The line on the x-axis at 1.0 represents the gene expression of control samples. (b) Bar plots representing fold-change values represented in the log2 scale showing gene expression in the brain of six-, nine-, and 12-month-old samples. Baseline shows expression in control samples. (c) Scattered-dot plot showing expression of genes involved in endoplasmic reticulum stress. * Expression is significantly different from WT (p ≤ 0.05). n.s., Nonsignificant.

Figure 4

Expression analysis of genes involved in calcium signaling. (a) Histograms representing relative mRNA expression of Snca, Ip3r, Nmdar, calm1, Vdcc, Erk, Ryr3, and Bad. Represented values are the mean and SD obtained from three individual experiments performed for each sample. The line on the x-axis at 1.0 represents the gene expression of control samples. (b) Bar plots representing fold-change values represented in the log2 scale showing comparative gene expression in the brain of six-, nine-, and 12-month-old samples. Baseline shows expression in the control sample. (c) Scattered-dot plot showing expression of genes involved in calcium signaling. * Expression is significantly different from WT (p ≤ 0.05). n.s., Nonsignificant.

Figure 5

Expression analysis of genes involved in mitochondrial disruption. (a) Histograms representing relative m RNA expression of Abad, Nmdar, Cx i–v, and Cycs. Represented values are the mean and SD obtained from three individual experiments performed for each sample. The line on the x-axis at 1.0 represents the gene expression of control samples. (b) Bar plots representing fold-change values represented in the log2 scale showing comparative gene expression in the brain of six-, nine-, and 12-month-old samples. Baseline shows expression in control samples. (c) Scattered-dot plot showing expression of genes involved in mitochondrial dysfunction. * Expression is significantly different to WT (p ≤ 0.05). n.s., Nonsignificant.

Figure 6

Expression analysis of genes involved in neuroinflammation and apoptosis. (a) Histograms representing relative mRNA expression of Tnf, Il1b, Casp 3, Casp 7, Casp 8, Casp 9, Casp 12, Nos1, Cysc, and Bid. Represented values are the mean and SD obtained from three individual experiments performed for each sample. The line on the x-axis at 1.0 represents the gene expression of control samples. (b) Bar plots representing fold-change values represented in the log2 scale showing comparative gene expression in the brain of six-, nine-, and 12-month-old samples. Baseline shows expression in control samples. (c) Scattered-dot plot showing expression of genes involved in calcium signaling. * Expression is significantly different to WT (p ≤ 0.05). n.s., Nonsignificant.

Figure 7

(a) Heat map showing comparison of all genes in this study expressed in diseased samples, divided into control, six-, nine-, and 12-month-old APP/PS1 transgenic mice. (b) Box plot showing comparison mean with SD of all genes involved in the onset of Alzheimer’s disease analyzed in three age groups. (c,d) Venn diagram representing the number of over- and underexpressed genes.

Figure 8

Comprehensive pathway of Alzheimer’s disease derived from the Kyoto Encyclopedia of Genes and Genomes (KEGG). This pathway shows a detailed summary of all the important genes involved in the molecular mechanisms in disease onset. Solid square boxes of different colors represent proteins while Colored squares without fill represents molecular events of the disease respectively.